[PATCH] iommu/dma: Add support for DMA_ATTR_SYS_CACHE

Isaac J. Manjarres isaacm at codeaurora.org
Sat Oct 26 00:43:36 UTC 2019

Currently, IOMMU_QCOM_SYS_CACHE exists to allow non-coherent
I/O masters on Qualcomm SoCs to upgrade to caching their
buffers in the outer-level/system cache on these platforms.
However, these masters are limited to managing the mapping
of these buffers themselves through the IOMMU framework,
as opposed to allowing the DMA-IOMMU framework to handle it,
since there is no DMA attribute that maps to the
IOMMU_QCOM_SYS_CACHE protection bit.

Thus, introduce DMA_ATTR_SYS_CACHE so that clients
can use the DMA-IOMMU layer to map their DMA buffers with
the correct memory attributes to allow the buffers to be
cached in the outer-level/system cache.

Signed-off-by: Isaac J. Manjarres <isaacm at codeaurora.org>
 drivers/iommu/dma-iommu.c   | 2 ++
 include/linux/dma-mapping.h | 8 ++++++++
 2 files changed, 10 insertions(+)

diff --git a/drivers/iommu/dma-iommu.c b/drivers/iommu/dma-iommu.c
index f321279..c433ece 100644
--- a/drivers/iommu/dma-iommu.c
+++ b/drivers/iommu/dma-iommu.c
@@ -369,6 +369,8 @@ static int dma_info_to_prot(enum dma_data_direction dir, bool coherent,
 	if (attrs & DMA_ATTR_PRIVILEGED)
 		prot |= IOMMU_PRIV;
+	if (attrs & DMA_ATTR_SYS_CACHE)
 	switch (dir) {
diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index 4a1c4fc..bdd4dcf 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -71,6 +71,14 @@
 #define DMA_ATTR_PRIVILEGED		(1UL << 9)
+ * DMA_ATTR_SYS_CACHE: This is a hint that non-coherent masters can use to
+ * tell the DMA-IOMMU layer to map their DMA buffers with the correct memory
+ * attributes that allow these buffers to be cached in an outer-level/system
+ * cache.
+ */
+#define DMA_ATTR_SYS_CACHE		(1UL << 10)
  * A dma_addr_t can hold any valid DMA or bus address for the platform.
  * It can be given to a device to use as a DMA source or target.  A CPU cannot
  * reference a dma_addr_t directly because there may be translation between
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